Solid perfluorocarbon polymers containing pendant sulfonic acid groups are useful catalysts for alkylating aliphatic or aromatic hydrocarbons, for decomposing organic hydroperoxides, such as cumene hydroperoxide, for sulfonating or nitrating organic compounds, and for oxyalkylating hydroxylic compounds.
A serious drawback to the commercial use of the perfluorocarbon sulfonic acid catalysts has been their high cost. As a means of reducing costs and improving effectiveness, films of the catalyst are desirable because they permit better control of catalytic activity and easier management of heats-of-reaction and in some instances, better selectivity. However, the solid perfluorocarbon sulfonic acids catalysts at the desired molecular and equivalent weights are difficult to work with because they are not thermoplastic, that is, they do not melt or soften on heating. In addition, such perfluorocarbon sulfonic acids having equivalent weights higher than about 900 and molecular weights in the range of about 50,000 to 100,000 daltons are substantially insoluble in all solvents. Polymers having equivalent weights below about 900 and in the lower range of molecular weights of about 50,000 daltons or lower are soluble in organic solvents i.e., ethanol, isopropanol, cyclohexanol and mixtures of organic solvents and water. It is known in polymer art that crosslinking polymer structures with free radicals and bifunctional compounds can substantially insolubilize low molecular weight polymers. It is also known that perfluorocarbon polymers tend to degrade in molecular weight and not crosslink with free radicals. The perfluorocarbon polymers containing pendant sulfonic acid groups form salts with metal ions which are less soluble in most solvents than the sulfonic acid polymer but the sulfonate salts of the perfluorocarbon polymer are not effective strong acid catalyst. There is no known way to deposit a soluble perfluorosulfonic acid polymer from a solution onto a support and then insolubilize the perfluorosulfonic acid polymer with retention of catalytic activity. The supported perfluorosulfonic acid catalyst of McClure et al. U.S. Pat. No. 4,038,213 made by depositing from a solution the soluble low equivalent weight, low molecular weight perfluorosulfonic acid resins are substantially limited in use to anhydrous systems i.e., hydrocarbons without organic solvents. An embodiment of the instant invention is an improved process for making supported perfluorosulfonic acid catalyst. This embodiment comprises conversion of the sulfonic acid groups to the quaternary ammonium or phosphonium salts to effect solubility of polymers having equivalent weights above 1,000 and molecular weights about about 50,000 daltons, deposition of the polymer containing the quaternary ammonium and phosphonium salts on a support, then, conversion of the ammonium and phosphonium salts to the sulfonic acid.
Another embodiment of the instant invention is a process for making new and improved supported perfluorosulfonic acid catalyst wherein the desired catalyst is obtained by first forming into the desired catalyst shape or coating on a substrate, as an intermediate or precursor material, a polymer of perfluorocarbon containing a sulfonyl fluoride group. Then the shaped polymer or coating is converted, to the degree desired, into the perfluorocarbon sulfonic acid catalyst to obtain a composite structure comprising a thin film of the perfluorosulfonic acid resin, a thin film of the intermediate or precursor material and a support. The forming is by heating if the intermediate polymer or precursor material is shaped as a thermoplastic, or by dissolving the intermediate polymer or precursor material in a solvent and then forming a coating on a substrate by evaporative deposition. The intermediate or precursor sulfonyl fluoride film serves to firmly bond the perfluorosulfonic acid catalyst to the support and to substantially insolubilize normally soluble low equivalent weight, low molecular weight perfluorosulfonic acid molecules on the surface of the perfluorosulfonyl fluoride or intermediate material, presumably by molecular entanglement of the polymer molecules and partial conversion of the intermediate material or sulfonyl groups on a polymer molecule to sulfonic acid groups. The sulfonyl fluoride polymer is substantially insoluble in all solvents except fluorocarbons.
The perfluorosulfonic acid catalyst are supported on solid supports primarily to maximize the surface area for reaction, maximize the number of sulfonic groups on or near the surface of the polymer for effective utilization of the catalyst facilitating minimum cost of catalyst and to modify engineering and mechanical properties to effect desired dimensional changes on solvation, fluids flow, heat removal, space time yield reaction, crush strength, etc. The preferred supported perfluorosulfonic acid catalyst comprises a film of a perfluorosulfonyl fluoride polymer precursor corresponding to a perfluorosulfonic acid polymer of 500 to 1,300 equivalent weight, preferably 900 to 1200 equivalent weight, deposited on a polymeric solid support, preferably a halocarbon or hydrocarbon polymer, by melt deposition, preferably by melt coextrusion, as a coating having a thickness of 0.1 mils to 2.0 mils, preferably 0.2 mils to 1.0 mils, and wherein said deposited perfluorosulfonyl fluoride polymer coating is converted to the corresponding perfluorosulfonic acid polymer to a depth of 0.01 mils to 1.0 mils, preferably to a depth of 0.05 to 0.5 mils.
The preferred supported catalyst of the instant process differ significantly from the supported catalyst of McClure et al. U.S. Pat. No. 4,038,213 in that the instant supported catalysts are attached to a substantially insoluble intermediate material or precursor material, a perfluorosulfonyl fluoride polymer, which firmly bonds the catalyst film to the support and substantially insolubilizes the normally soluble low equivalent weight, low molecular weight perfluorosulfonic acid molecules. The perfluorosulfonyl fluoride film may also serve as a substantially impermeable barrier to minimize permeation of reaction and regeneration fluids into the substrate. Prior to this invention, no practical way of making the preferred support perfluorosulfonic acid catalyst was known.